The present invention relates to a nuclear reactor control system and more particularly to a power monitoring device for a nuclear fusion reactor.
Fusion is the great name for the process in which nuclei of lightweight elements combine to form heavier and more tightly bound nuclei with the simultaneous release of significant amounts of energy.
For fusion to occur the interacting nuclei must come sufficiently close together to permit short-range nuclear forces to operate. This means that one or both nuclei must be accelerated to velocities sufficient to overcome the strong electrostatic repulsion that exits between particles having the same electrical charge. The velocities required are equivalent to particle "temperatures" of the order of hundreds of millions of degrees.
Various isolated thermonuclear fusion reactions have been observed in laboratory experiments; the ones that appear promising for controlled energy release are reactions between deuterium (D) and/or tritium (T) (the heavy isotopes of hydrogen), and possibly the reaction between deuterium and the rare isotope, helium-3. The electrostatic repulsion factor is minimized in reactions between these isotopes, since their nuclei have either a single or a double charge.
While the energy released by the fusion of two lightweight atoms is considerably less than the approximately 200 Million Electron Volts (MeV) released by the fission of a single heavy atom, the energy yield per unit of mass is comparable to (in the case of the D-D reactions) or greater than (in the case of the D-T reaction) than that obtained in fission.
Fusion reactors are in an early stage of development and no power monitoring system suitable for on-line plant use has been developed. Experimental devices such as the Princeton Large Torus (PLT) have used BF.sub.3 counters (such as described in J. D. Strachan, "The PLT Neutron Flux Measurement System," PPPL-TM-303, 1977) and activation foils (such as described in G. Zanki, J. D. Strachan, R. Lewis, W. Pettus, & J. K. Schmotzer, "Indium Activation Calibration of the 2.5 MeV Neutron Emission From PLT," Proc. Third APS Topical Conference on High Temperature Plasma Diagnostics, 1980) to deduce fusion reaction rates but these involve large calibration uncertanties and large time delays, respectively. Data from other plasma diagnostic instruments such as charge-exchange neutral atom detectors are also used for power inference but these are probably not feasible for commercial reactors because of radiation damage.
Moreover, monitoring systems based on BF.sub.3 or similar counters located some distance from the reactor and responding primarily to thermal and intermediate energy neutron have been considered and have been used on experimental devices. However, they are difficult to calibrate and their response is influenced by changes in the isotopic composition of the blanket during its lifetime and by changes in the detector surroundings.
Commercial fusion reactors will require reliable power monitors which are responsive to operational transients and which can be calibrated to provide an accuracy of a few percent. The sensors used in these systems must be essentially maintenance-free and must be capable of long-term operation without performance degradation due to radiation or electromagnetic effects. They should also be configured so as to yield information on the neutron wall loading distribution and, by inference, on the plasma position. They should also, of course, be as simple and inexpensive as possible and they should be unobstructive with respect to first-wall and blanket space utilization.